1. Technical Field
The present disclosure relates to a pulverizer.
2. Description of Related Art
In image forming methods such as electrophotography and electrostatic photography, visible images are formed by developing electrostatic latent images with toner. Toner is comprised of fine particles. Fine particles of toner are generally produced by melting and kneading raw materials of the toner, such as binder resins and colorants (e.g., dyes, pigments, magnetic materials), cooling and solidifying the kneaded product, pulverizing the solidified product, and classifying the pulverized product by size. In the above processes of pulverizing and classifying, a collision-type airflow pulverization-classification apparatus, such as an impact dispersion separator illustrated in FIG. 4A, can be used. In this apparatus, a pulverization object is accelerated by a jet flow and brought into collision with a collision plate to be pulverized. The pulverization product is then classified by size with a swirling airflow.
In a collision-type airflow pulverization-classification apparatus 107 illustrated in FIG. 4A, a powdery material is supplied from an input opening 102a and dispersed within a dispersion chamber 102. The powdery material is then anti-freely fluidized on a swirling airflow within a classification chamber 102c by the action of a secondary airflow 102b injected into the classification chamber 102c. The powdery material is classified into coarse particles and fine particles by the actions of the centrifugal and centripetal forces therein.
The fine particles are sent to a next process. The coarse particles fall down by their own weight to a returning chamber 108 and flow into a pulverizer 109 through a casing hopper 103.
In the pulverizer 109, the coarse particles 110 are sucked from a supply aperture 104, accelerated in an acceleration tube 114 of a pulverization nozzle 105, and brought into collision with a collision member 106 ahead to be pulverized. The pulverization product then goes up from a pulverization chamber 111 and flows into the dispersion chamber 102 again together with a newly-input powdery material input from an inlet opening 101, resulting in formation of a closed circuit pulverization.
One end of the acceleration tube 114 is connected to a jet nozzle 112 that supplies compressed air. The other end, i.e., an exit 115, of the acceleration tube 114 is facing the collision member 106. The coarse particles 110 are sucked from a supply opening 116 into the acceleration tube 114 by the flux of a high-speed airflow 113 that is a jet flow. The coarse particles are then conveyed to the pulverization chamber 111 by the injection of the high-speed airflow 113 and brought into collision with a collision surface 117 of the collision member 106 to be pulverized by the collision force.
Recently, image forming apparatuses have been improved in terms of image quality and colorization. In accordance with such improvements, there is a demand for a toner having a smaller particle size and a lower melting point. However, there are concerns that the production efficiency of such a toner is lowered in a case in which the toner is produced by an airflow-type pulverization-classification apparatus and the raw materials are fixedly adhered to such a production apparatus. These concerns also arise when the high-speed airflow 113 (i.e., jet flow) is neither sufficient nor uniform and therefore the pulverization object is dispersed within the acceleration tube 114 neither sufficiently nor uniformly.
JP-H08-052376-A (corresponding to JP-3219955-B2) discloses a collision-type airflow pulverizer illustrated in FIG. 4B. This apparatus is configured to satisfy the following inequation: L tan(θ/2)≧L1 tan(θ1/2)>(½)L tan(θ/2), wherein L represents the effective length of an acceleration tube 114, L1 represents ½ of the length L from the throat part along their common central line, θ represents the spread angle of the acceleration tube 114, θ1 represents twice of the angle formed between the common central line and a line connecting the throat part and one point on the inner peripheral surface of the acceleration tube 114 where the length from the throat point is L1.
JP-2010-155224-A discloses an airflow-type pulverization-classification apparatus illustrated in FIG. 5. The apparatus illustrated in FIG. 5 includes a jet nozzle 112 that injects a jet flow 113 in a pulverization chamber 111; a pulverization nozzle 105 having an acceleration tube 114, one end of which is connected to the front end of the jet nozzle 112 and the other end is opened to the pulverization chamber 111, and a supply tube 115 opened to the acceleration tube 114 to supply a pulverization object 110 to the jet flow 113; and a collision member 106 having a pulverization surface 117 disposed facing the jet nozzle 112. The pulverization object 110 along with the jet flow 113 is brought into direct collision with the pulverization surface 117 to be finely pulverized. A pressure gauge P is provided above the point where the supply tube 115 joins the acceleration tube 114. The pressure gauge P manages the supply condition of the pulverization object 110 to the acceleration tube 114.
JP-3016402-B2 (corresponding to JP-H04-326952-A) discloses a collision-type airflow pulverizer having an acceleration tube and a collision member. The acceleration tube is in the form of a de Laval nozzle provided with an inlet for high-pressure gas upstream from the throat part. A high-pressure gas introduced into the acceleration tube from the inlet conveys and accelerates a raw material. The collision member has a collision surface disposed facing the exit of the acceleration tube. The raw material is brought into collision with the collision member to be pulverized by the collision force. The collision surface has a cone-shaped tip whose apex angle is between 110 and 175 degrees.
JP-3114040-B2 (corresponding to JP-H07-60150-A) discloses a collision-type airflow pulverizer illustrated in FIG. 6. The apparatus illustrated in FIG. 6 includes an acceleration tube 201 that conveys and accelerates a pulverization object supplied through a high-pressure gas supply nozzle 203; and a pulverization chamber 213 within which the pulverization object is finely pulverized. Within the pulverization chamber 213, a collision member 211 having a collision surface is disposed with the collision surface facing an exit opening 210 of the acceleration tube 201. On the rear end of the acceleration tube 201, a pulverization object supply aperture is provided. The collision surface has a protruded central part 216 and an outer peripheral collision surface 217 having a cone shape. The pulverization chamber 213 has a side wall 215. The pulverization object having been pulverized by the collision member 211 is further brought into collision with the side wall 215 to be further pulverized. The apparatus satisfies the following inequation: 2(L1+L3)/3<L2<3·L3, wherein L1(≧0) represents the length of the high-pressure gas supply nozzle 203 having a throat diameter of a(>0), L2(>0) represents the length of the acceleration tube 201, and L3(>0) represents the shortest distance between the apex of the protruded central part 216 and the outer peripheral collision surface 217. The apparatus further satisfies the following inequations: 0°≦θ1≦20° and a +2·L1 tan(θ1/2)<b<c/2, wherein θ1 represents the spread angle of the high-pressure gas supply nozzle 203, b represents the throat diameter of the acceleration tube 201, and c represents the diameter of the bottom surface of the protruded central part 216. The apparatus further satisfies the following inequations: 0°≦θ2≦20° and b+2·L2 tan(θ2/2)<c<d, wherein θ2 represents the spread angle of the acceleration tube 201 and d represents the diameter of the outer peripheral collision surface 217. The apparatus further satisfies the following inequations: 0°<θ3<90°, 0°<θ03<θ4<90°, and d+2·L3 tan(θ3/2)>e>d, wherein θ3 represents the apex angle of the protruded central part 216, θ4 represents the apex angle of the outer peripheral collision surface 217, e represents the diameter of the pulverization chamber 213, and c=2·L3 tan(θ3/2).
JP-3219918-B2 (corresponding to JP-H07-136543-A) discloses a pulverizer including a jet nozzle that injects a jet flow in a pulverization chamber; an acceleration tube, one end of which is connected to the front end of the jet nozzle and the other end is opened to the pulverization chamber; a supply tube opened to the acceleration tube to supply a pulverization object to the jet flow; and a collision member having a pulverization surface disposed facing the jet nozzle. The pulverization object along with the jet flow is brought into direct collision with the pulverization surface to be finely pulverized. The supply tube has an introduction part vertical to the acceleration tube; and an injection part, one end of which is connected to the introduction part and the other end is opened to the acceleration tube, slanted in the direction of the jet flow. The injection part includes a first air supply opening opened to the injection part; a first air supply means for supplying the air to the injection part through the first air supply opening; a second air supply opening opened to the injection part; and a second air supply means for supplying the air to the injection part through the second air supply opening. The central axis of the second air supply opening is parallel to that of the injection part.
JP-H03-086257-A discloses a collision-type airflow pulverizer including an acceleration tube that conveys and accelerates a powder material by a high-pressure gas; a pulverization chamber; and a collision member that pulverizes the powder material injected from the acceleration tube by a collision force. The collision member is provided within the pulverization chamber with facing the exit of the acceleration tube. The acceleration tube is provided with a powder material inlet. A secondary air inlet is provided between the powder material inlet and the exit of the acceleration tube. This apparatus satisfies the following inequations: 0.2≦y/x≦0.9 and 10°≦Ψ≦80°, wherein x represents the distance between the powder material inlet and the exit of the acceleration tube, y represents the distance between the raw material inlet and the secondary air inlet, Ψ represents the installation angle of the secondary air inlet to the acceleration tube in the axial direction of the acceleration tube.
JP-2000-140675-A discloses pulverizers illustrated in FIGS. 7A to 7D. A compressed gas is supplied to an acceleration nozzle 312 through an inlet 313, throttled at a throat part 314 provided downstream from the inlet 313, and expanded at a diffuser part 315 provided downstream from the throat part 314 to form a jet current. A pulverization object is supplied to the acceleration nozzle 312 from a pulverization object supply opening 317 of a hopper 309. The pulverization object is injected from the exit of the acceleration nozzle 312 and brought into collision with a collision member 304, facing the exit, to be pulverized. The inner surface of the throat part 314 is contiguous with those of the inlet 313 and the diffuser part 315, forming a smooth arc-like inner surface. A straight part 316 is further provided at an exit side of the diffuser part 315. The cross-sectional area of the straight part 316 in the axial direction is constant over the entire length thereof. According to one example, L1=55 mm, L2=238 mm, L3=56 mm, D1=70 mm, D2=37 mm, θ1=30°, θ2=11°, and r=33 mm are satisfied.
In the above-described arts, generally, a pulverization object is supplied from a hopper to an acceleration tube through a supply aperture and accelerated by a jet flow in the acceleration tube. The ability of pulverizing pulverization object generally improves when the acceleration speed of the jet flow is kept constant during the supply of pulverization object to the acceleration tube.
In the related arts, the supply aperture is generally connected to the acceleration tube forming a relatively large angle therebetween. This means that the cross-sectional area of the supply aperture is relatively small and therefore the ability of supplying pulverization object to the acceleration tube is relatively low. In a case in which the pulverization object is pulverized into very fine particles, the ability of pulverizing pulverization object is more lowered because the ability of supplying pulverization object is lowered by changes in bulk density of the pulverization object, which may cause clogging of the hopper.